METHODS OF STAINING. 421 



bottom of the dish, and the sections to be stained are transferred 

 from distilled water to the dye and distributed upon the paper in 

 such a way that they do not lie over each other. The dye acts 

 very slowly, twenty-four hours being none too long for good results. 

 If the staining be hastened by using a stronger solution, it suffers 

 in sharpness. After staining, the sections are thoroughly washed 

 in distilled water, and may then be subjected to a nuclear dye, such 

 as hsematoxylin. The proper acidulation of the diluted dye is of 

 importance for the success of this method. If the solution is not 

 sufficiently neutralized, the sections will not be stained ; if it is too 

 acid, precipitation of the carmine will take place. 



3. Alum-carmine. 



Alum, 5 grams. 



Distilled water, 100 cc. 



Carmine, " No. 40," 2 grams. 



The alum is dissolved in the water with the aid of heat, the 

 carmine then added, and the mixture kept at the boiling-point for 

 about half an hour. It is then allowed to cool and filtered into the 

 stock-bottle. Two or three drops of deliquesced carbolic acid may 

 be added to prevent the development of fungi. 



Sections are stained in the undiluted, but filtered, dye for at least 

 five minutes. There is no danger of over-staining. It is a pure 

 nuclear stain, coloring the chromatin red. After staining, the sec- 

 tions are either washed, and are then ready for dehydration, or 

 they may receive a counterstain with picric acid, coloring the tissues 

 a diffuse yellow. This may be most readily accomplished by adding 

 a few small crystals of picric acid to the first dish of dehydrating 

 alcohol (see p. 428). 



4. Borax-carmine. 



Borax, 4 grams. 



Distilled water, 100 cc. 



Carmine, " No. 40," 3 grams. 



Alcohol, 70 per cent., 100 cc. 



The borax is dissolved in the water by warming, and the solution 

 allowed to cool ; the carmine is then stirred in and the alcohol added. 

 After standing twenty-four hours the solution is filtered into the 

 stock-bottle, a process that is exceedingly slow. 



